Study of sound transmission through muffler sidewall by analytical, numerical and experimental methods

In addition to the sound radiated from the tail pipe, the sound transmitted through the sidewall can also be a major contributor to the muffler noise. We developed analytical, numerical and experimental methods to evaluate the sound transmitted through the muffler sidewall. The analytical method directly solves coupled vibro-acoustic equations of the muffler using a simplified model to calculate the transmission loss through the sidewall. The numerical method utilizes the finite element-boundary element method and solves the problem using the actual geometry. The experimental method measures noise level differences for the actual muffler. The results from the three methods are compared to understand proper applications of respective models. It is shown that the sidewall performance is important in the mid-frequency range, 600 Hz–950 Hz for the prototype muffler. Design parameter study utilizing the numerical method showed that the sidewall performance follows the mass-law in this frequency range, i.e. doubling the thickness provides a 6-dB noise reduction.